Low-friction moving interfaces in micromachines and nanomachines

ABSTRACT

A low-friction device having a moving interface comprising first and second members. Each of the members has a maximum dimension of about 100 μm or less between any two points. At least the first member is formed of diamond and the first and second members are in sliding contact or meshing contact.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 11/342,061 filed Jan. 27, 2006, which is a continuation applicationof U.S. application Ser. No. 10/925,866 filed Aug. 24, 2004, which is acontinuation application of U.S. application Ser. No. 10/094,149 filedMar. 7, 2002, which claims priority from the following provisionalapplication, the entire disclosures of which are incorporated byreference in their entirety for all purposes:

-   -   U.S. Application No. 60/287,677, filed Apr. 30, 2001 by        Victor B. Kley for “Scanning Probe Microscopy and        Nanomachining.”

The following six U.S. patent applications, were filed concurrently withU.S. application Ser. No. 10/094,149 and the disclosure of each otherapplication is incorporated by reference in its entirety for allpurposes:

-   -   U.S. patent application Ser. No. 10/093,842, filed Mar. 07, 2002        by Victor B. Kley for “Nanomachining Method and Apparatus”;    -   U.S. patent application Ser. No. 10/094,411, filed Mar. 07, 2002        by Victor B. Kley for “Methods and Apparatus for Nanolapping”;

The following U.S. patents are incorporated by reference in theirentirety for all purposes:

-   -   U.S. Pat. No. 6,144,028, issued Nov. 07, 2000 to Victor B. Kley        for “Scanning Probe Microscope Assembly and Method for Making        Confocal, Spectrophotometric, Near-Field, and Scanning Probe        Measurements and Associated Images;”    -   U.S. Pat. No. 6,252,226, issued Jun. 26, 2001 to Victor B. Kley        for “Nanometer Scale Data Storage Device and Associated        Positioning System;”    -   U.S. Pat. No. 6,337,479, issued Jan. 08, 2002 to Victor B. Kley        for “Object Inspection and/or Modification System and Method;”        and    -   U.S. Pat. No. 6,339,217, issued Jan. 15, 2002 to Victor B. Kley        for “Scanning Probe Microscope Assembly and Method for Making        Confocal, Spectrophotometric, Near-Field, and Scanning Probe        Measurements and Associated Images.”    -   U.S. Pat. No. 6,752,008, issued Jun. 22, 2004 by Victor B. Kley        for “Method and Apparatus for Scanning in Scanning Probe        Microscopy and Presenting Results”;    -   U.S. Pat. No. 6,787,768, issued Sep. 7, 2004 by Victor B. Kley        and Robert T. LoBianco for “Method and Apparatus for Tool and        Tip Design for Nanomachining and Measurement”.    -   U.S. Pat. No. 6,802,646, issued Oct. 12, 2004 by Victor B. Kley        for “Low Friction Moving Interfaces in Micromachines and        Nanomachines”; and    -   U.S. Pat. No. 6,923,044, issued Aug. 2, 2005 by Victor B. Kley        for “Active Cantilever for Nanomachining and Metrology”;

The disclosure of the following published PCT application isincorporated by reference in its entirety for all purposes:

-   -   WO 01/03157 (International Publication Date: Jan. 11, 2001)        based on PCT Application No. PCT/US00/18041, filed Jun. 30, 2000        by Victor B. Kley for “Object Inspection and/or Modification        System and Method.”

BACKGROUND OF THE INVENTION

This application relates generally to micromachines and nanomachines andmore specifically to devices providing low-friction rotational andtranslational interfaces for micromachine and nanomachine contacts.

Micromachines and nanomachines are poised to solve mechanical problemsat the molecular and atomic level. Such machines may solve problems inenvironments were other devices, such as electronic devices, fail. Forexample, microscale mechanical memories may be of use in environments,such as space, in which semiconductor based devices have high faultrates due to high-energy cosmic radiation. Further, microscalemechanical machines may be of surgical use, reaching areas of the bodynot otherwise accessible or manipulable by traditional surgical toolsand techniques.

At small scale, for example in the hundreds and tens of micron range andbelow, mechanical elements exhibit problematic behavior that either 1)does not arise or 2) is of little consequence at relatively largerscale. For example, meshed gears in macroscale machines do not tend toexhibit problems due to stiction, which is the sticking and fusing ofdifferent elements or portions of elements into a union. However, atsmaller scale, such problems can arise.

Lithographic techniques have been deployed to make relatively smallmechanical devices, for example, relatively small gears etched fromsilicon wafers. However, such relatively small silicon gears have atendency to stick and fuse to each other. If such gears are inmechanical motion when stiction between the gears occurs, the gears maygall each other or worse tear each other apart.

Lubricants have been applied to relatively small mechanical interfacesin an attempt to limit friction, stiction, and galling. However, likesolid bits of matter of relatively small scale, liquids at relativelysmall scale also exhibit problematic behavior that would be of littleconsequence at relatively larger scale. For example, surface tensioncauses relatively small quantities of liquid to form small droplets thattend not to flow across a surface, thus limiting a lubricant'seffectiveness.

Consequently, new microscale and nanoscale devices are sought whichprovide for improved performance.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention low-friction moving interfaces inmicromachines and nanomachines include low-friction sliding interfaces.In one aspect of the invention, a device has first and second members insliding contact. Each the members has a maximum dimension of about 100μm or less between any two points and one of the first and secondmembers is formed of diamond. In another aspect of the invention, adevice has a toothed member and a tooth-engaging member in meshingcontact. Both the toothed member and tooth-engaging member havedimension of about 100 μm or less between any two points and one of thetoothed member and tooth-engaging member is formed of diamond.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the temperature of a diamond-silicon dynamicinterface for a relatively small diamond according to a mathematicalmodel of the interface;

FIG. 2 is an overall perspective view of a mechanical device having alow-friction moving interface according to an embodiment of the presentinvention;

FIG. 3 is a schematic cross-sectional view of another mechanical devicehaving a low-friction moving interface according to another embodimentof the present invention;

FIG. 4 is a schematic cross-sectional view of another mechanical devicehaving a low-friction moving interface according to another embodimentof the present invention;

FIG. 5 is a schematic cross-sectional view of another mechanical devicehaving a low-friction moving interface according to another embodimentof the present invention; and

FIG. 6 is an overall perspective view of another mechanical devicehaving low-friction moving interfaces according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The following description sets forth embodiments of low-friction movinginterfaces in micromachines and nanomachines according to the invention.Embodiments of the invention can be applied to sliding and/or meshingmechanical contacts.

Diamond is a very slippery crystal. Diamond in mechanical contact withcrystals such as diamond itself or silicon exhibits relativelylow-frictional heating and has a tendency not to fuse with itself orsilicon. Further, the flash temperature of diamond-silicon interfaces isrelatively high. The flash temperature is that at which bodies infrictional contact tend to gall each other. The flash temperature ofvarious interfaces can be estimated by taking into account, for example,the speed at which surfaces move with respect to each other and theforces at the interface. For example, see “Tribology and Mechanics ofMagnetic Storage Devices,” publisher Springer, pp. 366-411, by Bhushanin which a general formalism is developed to calculate flashtemperatures.

FIG. 1 is a graph of a mathematical modeling of the temperature of adynamic diamond-silicon interface at various interface forces andvelocities. The diamond-silicon interface modeled is that of a diamondrod having a flat circular end sliding across a planar piece of silicon.The diameter of the flat circular end of the rod is about 50 nm at theinterface. As indicated by the graph, the temperature of the diamond andsilicon forming the interface rises from frictional heating as the forceand/or velocity of the diamond and silicon increase. Pinnacle 110 at thetop right of the graph represent the flash temperature of the interface.As can be seen, the flash temperature, is between 900° C. and 1000° C.The interface force of the diamond on silicon at the flash temperatureis between 275 millinewtons and 300 millinewtons and the velocity of thesurfaces relative to each other is about 500 millimeter/second. Forcesand velocities in these ranges are relatively high indicating thegeneral durability of the interface. While the graph represent only asingle geometric interface of diamond and silicon in frictionalcontract, an impetus is created for the manufacture of diamond-siliconmechanical interfaces of relatively small scale.

Described below are various embodiments where two members engage eachother in different ways, referred to as sliding contact and meshingcontact. These types of interaction will be defined below in connectionwith the specific embodiments. In these embodiments, both of the membersmay be diamond or one of the members may be diamond with the otherbeing, for example, silicon, quartz, a III-V material such as galliumarsenide, and the like. While substances such as silicon and galliumarsenide are of limited mechanical use at macroscale dimensions (e.g.greater than 1 millimeter) due to their fragility, such substancessuffer less from fragility at relatively smaller scales, (e.g. 100 μm).At such small scales, each of the aforementioned materials in suchcontact with diamond provides for devices that have relatively lowfriction and are relatively mechanically sound. Further, each of theaforementioned materials has a relatively high flash temperature insliding contact with diamond, for example, as high as 900° C. and above.Thus at normal operating temperature, (e.g., 300° C.) such materialstend not to gall each other.

Embodiments having Sliding Contact

A “sliding contact” is defined herein as a first member that is indynamic frictional contact with a second member, such that the firstmember and second member have surfaces that are in smooth continuouscontact.

FIG. 2 is an overall perspective view of a mechanical device 200 havinga low-friction moving interface 210 according to an embodiment of thepresent invention. The mechanical device includes a first member 215that has a circular aperture 222. Portions of the aperture are indicatedin phantom view. The aperture has a surface denoted by reference numeral225. The mechanical device includes a second member 250 in the shape ofa spindle having a rounded surface 252, portions of which are shown inphantom. As shown, the second member is fitted into the aperture.Low-friction moving interface 210 is identified as the areas at whichthe aperture surface and the second member are in sliding contact. Thefirst member and second member may have a rotational degree of motionwith respect to each other (as indicated by double-headed arrow 262), atranslational degree of motion with respect to each other (as indicatedby double-headed arrow 268), or both.

First member 215 and second member 250 may each be a single ormulticrystalline structure. For example, first member 215 may be asingle diamond crystal or a polycrystalline diamond.

The first and second members may be fabricated using a variety oftechniques. For example, a member comprising silicon may be etched froma silicon wafer using known lithographic techniques or may be cut from asilicon wafer using cutting and sweeping techniques discussed in theabove referenced U.S. Patent Application for “Nanomachining Method andApparatus,” Attorney Docket No. 020921-001430US. Alternatively, a membercomprising silicon may be formed by lapping techniques such as thosediscussed in the above referenced U.S. Patent Application for “Methodsand Apparatus for Nanolapping,” Attorney Docket No. 020921-001450US.Each of these fabrication techniques is similarly applicable to diamondmembers, quartz members, and the like. Those of skill in the art willknow of other useful fabrication techniques.

First member 215 may be coated into the aperture of another device suchas a disk. A first member so positioned is commonly referred to as abushing. For example, a first member comprising diamond may be coatedinto an aperture in a silicon disk. A first member so positioned may beformed, for example, by first forming a diamond-like carbon layer in theaperture and second growing a diamond onto the diamond-like carbonlayer. Diamond-like carbon may be coated into an aperture via a vacuumarc process or via ion-beam techniques and grown using plasma-enhancedchemical vapor deposition. Those of skill in the art will know otheruseful coating processes for diamond-like carbon. Diamond can alsosubsequently be grown onto the diamond-like carbon in a diamond-anvilcell or other high-pressure device.

According to a specific embodiment of the invention, each of the firstand second members has a maximum dimension of about 100 μm or lessbetween any two points. According to another embodiment, each of thefirst and second members has a maximum dimension of about 5 μm or lessbetween any two points.

FIG. 3 is a schematic cross-sectional view of a mechanical device 300having a low-friction moving interface 310 according to anotherembodiment of the present invention. The mechanical device includes afirst member 315 that has a round socket 322, which is defined bysurface 326. Mechanical device 300 includes a second member 350 that hasan arm portion 352 and a ball end 354. The ball end of the second memberis in sliding contact with surface 326. Such a configuration is commonlyreferred to as a ball-and-socket joint.

For consistency and clarity, a particular coordinate system will beshown and referred to. FIG. 3 is considered to lie in the x-y plane, andthe z-axis will be considered to extend out of the page. In accordancewith standard symbology, an axis extending out of the page will bedenoted by a dot in a circle while an axis extending into the page willbe denoted by a + in a circle. The cross-sectional view of FIG. 3 thusshows mechanical device 300 extending laterally in the x-y plane. Inmost instances, references to direction and orientation that mention anaxis (e.g., the x-axis) or a plane (e.g., the x-y plane) should beconsidered to include lines parallel to that axis, or planes parallel tothat plane

First and second members 315 and 350 may have a variety of rotationaldegrees of motion with respect to each other, for example, member 350may rotate relative to member 315 about the z-axis, the x-axis, or anyaxis laying between the z and x-axes.

FIG. 4 is an overall perspective view of a mechanical device 400 havinglow-friction moving interfaces 410 according to an embodiment of thepresent invention. The mechanical device includes a first member 415 inthe shape of a plate, and a second member 420 having a slot 422. Aportion of first member 415 is inserted into slot 422. The first memberspins such that portions of its surfaces 423 and 425 are in slidingcontact with surfaces 427 and 429, respectively.

According to a specific embodiment of the invention, each of the membershas a maximum dimension of about 100 μm or less between any two points.According to another embodiment, each of the members each has a maximumdimension of about 5 μm or less between any two points. First and secondmembers 410 and 420 may be fabricated by a variety of processes such asthose described above for the fabrication of mechanical device 200 shownin FIG. 2.

Mechanical devices having components (e.g., diamond plate and siliconslotted member) providing low-friction translational contact aredeployable for a variety of tasks. For example, mechanical device 400may be of use as a fluid pump. The low-friction moving interface candrag a fluid between ends of the slot, thus providing pumping. Further,such a device, made of say diamond and silicon or diamond and diamond,provides for tremendous translational rates. For example, a diamondplate in a silicon slot of the dimension discussed above may be turnedat millions or more revolutions per second prior to reaching the flashtemperature.

Each of devices 200, 300, and 400 may be bearing type devices, whereinone of the members provide support, guidance, and reduces the frictionof motion between the other member and moving or fixed machine parts(not pictured in FIGS. 2, 3, or 4). Other moving or fixed machine partsmay include, for example, a housing (e.g., a journal box) containing oneof the devices, or additional members in sliding contact devices 200,300, and 400.

Embodiments having Meshing Contact

A “meshing contact” is defined herein as a “toothed member” being infrictional contact with a “tooth-engaging member,” such that the toothedmember meshes with the tooth-engaging member to transmit motion or tochange direction or speed.

FIG. 5 is a schematic cross-sectional view of a mechanical device 500having a low-friction moving interface 510 according to anotherembodiment of the present invention. The mechanical device includes agear 515 (an example of a toothed member) that has a plurality of gearteeth 520 and includes a rack 550 (an example of a tooth-engagingmember) that has a plurality of gear teeth 555. As shown, gear teeth 520and gear teeth 555 are in meshing contact. Mechanical device 500provides for two types of motion: (a) the rack may be moved laterallyalong the x-axis causing the gear to rotate about the z-axis, or (b) thegear may be rotated causing the rack to be translated. Translationdevice 560 coupled to rack 550 may provide such translations of therack. Translation device 560 may include a variety of devices, such as,piezoelectric transducers, thermal expansion/contraction devices,mechanical actuators, and the like. Further, such translation devicesmay be coupled to both ends of the rack for further control.

While rack 550 is shown to have teeth that extend beyond the regionwhere the gear and rack mesh, the teeth may extend a lesser amount, forexample, the teeth may be limited to the region where the gear and rackmesh.

According to a specific embodiment of the invention, each of the gearand rack has a maximum dimension of about 100 μm or less between any twopoints. According to another embodiment, each of the gear and rack has amaximum dimension of about 5 μm or less between any two points. Gearsand racks made of materials such as those discussed may be fabricated bya variety of processes such as those described above for the fabricationof mechanical device 200 shown in FIG. 2.

FIG. 6 is a schematic cross-sectional view of a mechanical device 600having a low-friction moving interface 610 according to anotherembodiment of the present invention. The mechanical device includes agear 615 (an example of a toothed member) that has a plurality of gearteeth 620 and includes a worm gear 650 (an example of a tooth-engagingmember) that has a thread 655. As shown, gear teeth 620 and thread 655are in meshing contact. Mechanical device 600 provides for two types ofmotion: (a) worm gear 650 may be rotated about the x-axis causing gear615 to rotate about the z-axis, or (b) gear 615 may be rotated about thez-axis causing the worm gear to rotate about the x-axis.

Both the gear and/or rack shown in FIG. 5 and the gear and/or worm gearshown in FIG. 6 may be coupled to a devices 200, 300, or 400 shown inFIGS. 2, 3, and 4. For example, the second member 252 (FIG. 2) having aspindle shape may be coupled to the center of rotation of gear 515and/or worm gear 550. Both gear 610 and worm gear 650 have similarmaximum dimension as those of gear 510 and rack 550 shown in FIG. 5 andcan be fabricated by similar methods.

Conclusion

While the above is a complete description of specific embodiments of theinvention, various modifications, alternative constructions, andequivalents by be used. For example, diamond-silicon, diamond-diamond,and the like may be variously configured while still providing lowstiction, low galling, and relatively high flash temperature devices.For example, device 200 may have a first member 215 that has a trenchinstead of an aperture in which the second member is in sliding contact.Further, diamond-silicon, diamond-diamond, and the like meshinginterfaces may include, for example, gear on gear interfaces in additionto gear on rack/worm gear interfaces. Therefore, the above descriptionshould not be taken as limiting the scope of the invention a defined bythe claims

1. A low-friction device having a moving interface, the low-frictiondevice comprising first and second members wherein: each of the membershas a maximum dimension of about 100 μm or less between any two points;at least the first member is formed of diamond; and the first and secondmembers are in sliding contact.